Why does not come out of bird eggs

Budgerigar lies on the eggs for 20 days, called the incubation period, and at the end of this period, the offspring comes out of the egg. There are some conditions for the output of the puppy:

1- Male must meet with a budgerigar before ovulation.

2- Eggs should remain at fixed temperature in incubation, the egg breaks when it cools.

3- If you have too much eggs for your bird, those who are exposed will be broken, the incubator can be used for extra budgerigar eggs.

4- Some people produce artificial hatching machines with a simple lamp editor, but in this case it is difficult to fix the heat.